Reap

Reap[expr] gives the value of expr together with all expressions to which Sow has been applied during its evaluation. Expressions sown using Sow[e] or Sow[e,tagi] with different tags are given in different lists.

Reap[expr,patt] reaps only expressions sown with tags that match patt.

Reap[expr,{patt1,patt2,…}] puts expressions associated with each of the patti in a separate list.

Reap[expr,patt,f] returns {expr,{f[tag1,{e11,e12,…}],…}}.

Examples

Reap[Sow[1]; Sow[2]; Sow[3]]
(* {3, {{1, 2, 3}}} *)

Reap[Sow[a, x]; Sow[b, y]; Sow[c, x], x]
(* {c, {{a, c}}} *)

Please visit the official Wolfram Language Reference for more details.